Fatigue tests were conducted on a lower bainite steel, which is applicable to vehicle components due to good resistance against crack propagation, under mode I and mixed mode conditions. The fatigue crack propagation path and fracture criterion were investigated from the results of the tests. The crack growth rates were evaluated in terms of effective stress intensity factor range, using both the extended and projected crack lengths. The initial crack branching angles with variation of the ratio of K_I/K_(II) are found to be in good agreement with the maximum tangential stress criteria. The effective stress intensity factor range with the result of growth rate under mode I loading condition can predict the crack growth rate under mixed mode loading conditions. Extended crack length rather than projected crack length is appropriate for the presentation of the crack growth rate under the mixed mode loading conditions.